Buying a used MM Fender and replace the pickups?

I'm a bit in debate. I want to buy a better bass then my current Aria. Seems to me, it isn't hard to imagine eh?

I think the MM plays and sounds great and offers a lot, considering its price. I have replacement pickups in my Aria, the Music Man (toggle-switch for parallel/series/single coil operation) and J-vintage of Bartolini. I really like the specifications of the Marcus Miller bass (Bart preamp, nice pickups, BadAss Bridge..etc..) but I was thinking, that perhaps I could swap the pickups -I can't imagine it's going to cost a lot- and then having the perfect bass for me instead.

All sounds included!

Perhaps anyone has something to say about this... simply a do or a don't, and why?

I just liked the dry sound of the Music Man pickup in series. Hard to get with only one bridge pickup. I've tried a MM bass before and it really pleased me, but because I have those pickups on a cheap-ass bass, I thought I could re-use them.

My buddy has a 2001 mex jazz bass that he put vintage custom shop p-ups(100.00$)and a bad ass bridge(50.00$)and had a frett leveling and re-crown done as well.
Now mexican fenders are not all equal,and his is one of the best made ones I have ever played,It was dumb luck that he came across this bass to begin with.
If you find one that is made well then they are worth adding some up-grades,I had a 98 model that was a P.O.S. that would'nt play well no matter what I had done to it,the neck moved all the time,the fretts would stick out the side of the neck,it hated to stay in tune from one song to the next, never mind from one day to the next ETC.
So with this in mind take your time and look through a few different stores,play as many different basses as you can to find one that feels right to you(you will know it when you find it,and if you are'nt that skilled with bass searching bring a friend who is).
For 400.00$ to buy the bass and 250.00$ in up-grades and labor,you mite find yourself with a bass that will be a joy to play(or spend 600.00$ outright and buy an american US 1 BASS and then make some adjustments )its a crap shoot either way you look at it !